Masters Theses

Date of Award

8-2023

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Nicholas Brown

Committee Members

Ivis C. Gore, Jamie Coble

Abstract

Integrated Energy Systems (IES) serve as a method of cogeneration for both electrical and thermal energy. The cogeneration of both energies has served as a method of reducing waste heat and improving the efficiencies of the processes that operate within the IES grid. Thermal energy storage and distribution within an IES is a key point for an IES which uses a nuclear reactor as the main form of thermal energy provider. Desalination has been a common endothermic process used within an IES grid, mainly due to the low thermal demands required for such a process, and the wide variety of applications the produced water has, either as drinking water, industrial heating, or other such uses.

With the growing interest in the feasibility of nuclear reactors used in applications alternative to electrical generation, the history of previous work has left us with important lessons for the future. The Aktau Nuclear Power Plant (NPP), along with other nuclear desalination operations in Japan and other countries, has laid the groundwork for nuclear IES operations. The lessons learned from the low-temperature desalination process provide key framework for high-temperature IES operations like nuclear hydrogen production. The Aktau NPP was the only Molten Salt Reactor (MSR) operated within an IES, providing an additional demand for a review for future IES work with an advanced reactor.

Hydrogen production, especially nuclear hydrogen production, has also been experiencing an increase in interest. This is due to the ability of hydrogen energy to reduce carbon emissions in the wide range of applications that produce hydrogen. While electrolysis is currently the hydrogen production method that has the most interest, thermochemical cycles also show promise as production methods competitive with electrolysis. Sulfur-based thermochemical cycles like the Sulfur Iodine and Hybrid Sulfur (HyS) cycles are among the most promising, and previous work has established them as cycles that are the most favorable for nuclear hydrogen production, and as endothermic processes capable of integration within a nuclear IES.

Previous work has shown that the HyS cycle can be competitive with electrolysis from an efficiency standpoint. For future IES grid evaluations, a reduced and simplified model of the complex sulfuric acid decomposition reaction is necessary. This model can serve the purpose of providing a wide variety of outputs, including efficiency and energy demand as well as conversion, based on only a few inputs. Creating an agnostic model capable of use with a variety of different types of nuclear reactors, heating fluids, and IES grid setups, while providing results comparable to previous work.

The reduced order model was able to generate results based on temperature, pressure, and weight fraction sulfuric acid that agreed with previous work. Generating an operational range for weight fraction between 0.63 and 0.89 weight fraction sulfuric acid that agreed with past work and met efficiency goals. High temperatures and high pressures saw the best efficiencies as well, with lower temperatures and high pressures becoming more inefficient than lower temperatures and lower pressures.

Outside of the operational parameters the model produces results that are overestimations when compared to previous work. However, these operational ranges are already outside of desirable conditions and therefore unlikely to be used in normal, steady-state conditions. The assumptions that play key roles in these overestimations have been identified for moving forwards with a more complex model for transient operations, and future work using the methodology outlined in this thesis is expected to provide key information for advanced nuclear reactors powering hydrogen production within an IES.

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